War index help

I just wanted to know,what is the quickest or mos efficient way to raise your war index.

I assume your talking about war situation index, in which case the purchasing of defense fortifications raises it nicely.

where do you buy fortifications?

In the top of your main country page there are several tabs, choose "Trade" illustrated with a hand holding a bag.
Then click on the option "Products on stock: bull and sell", a list of all products that your country have in stock will be displayed; search for "Defense Fortifications" and click on "buy".
I suggest buy only you need in Defensive fortifications, in that way, you can keep your country financial index healthy.
Sorry for my bad English. Cheers!